Field of Invention
This invention relates to the novel use of nitrogen-containing compounds having a melting point greater than the melting point of urea and the use of these compounds as plasticizers for peptide-based biopolymers. The peptide-based biopolymers with the nitrogen-containing plasticizer can be used as fertilizer, animal feed, and a substitute for hydrocarbon-based plastics.
Description of the Prior Art
In polymer chemistry, plasticizers are added to ease compounding and processing procedures and are used to produce the desired product properties. In some instances, the addition of a plasticizer to a material results in a lowering melting point of the plasticizer/material combination compared to the melting point for both the plasticizer and the material, individually. For example, outside of polymer technology, tin has a melting point of 231° C. and lead has a melting point of 327° C.; yet a Sn—Pb mixture (such as a solder) melts at approximately 182-183° C.
Peptide-based biopolymers, such as keratin and silk, have limited utility as biopolymers because of the difficulty of working with them as a biopolymer. Many peptide-based biopolymers are cross-linked via disulfide bonds between the cysteines within the biopolymer's amino acids. These disulfide bonds impart strength and rigidity to the biopolymers. However, to use these biopolymers, one must often break the disulfide bonds using high temperature, acids, alkalines, redox agents, enzymes, urea, or a combination thereof. Yet such treatments can also break the peptide bonds between the amino acids resulting in the peptide-based biopolymer becoming too soft or decomposing. In addition to disulfide bonds, the secondary structure of peptide-based biopolymers can include large amounts of α-helix and/or β-sheet formations which also strengthen the peptide-based biopolymer because of hydrogen bonding between the amide and carbonyl groups of different amino acids within the helix or between different strands of the sheet. Breaking these hydrogen bonds without decomposing the biopolymer can be difficult.
While urea is extremely useful in degrading disulfide bonds, under normal processing conditions, urea breaks down into ammonia, a toxic substance under certain conditions. As such, OSHA requires (i) isolating every extruder containing urea and biopolymers from other equipment in the facility, and (ii) workers must wear protective breathing gear while operating extruders containing urea and biopolymers. Additionally, ammonia corrodes expensive metal molds. Finally, ammonia sublimates under biopolymer processing conditions; thus resulting in ammonia bubble formation in the pellets which then can pop like popcorn during the extrusion process. As such, urea is a sub-optimal plasticizer for peptide-based biopolymers.
Hydrocarbon-based polymers have previously been used as plasticizers for peptide-based biopolymers. However, using hydrocarbon-based polymers as a plasticizer defeats the goals of using biodegradable chemicals and using chemicals that are not made from petroleum, a scarce commodity.
U.S. Pat. No. 7,006,995 describes using ethylene glycol ((CH2OH)2), propylene glycol (CH3OHCHOHCH2OH), glycerol ((CH2OH)2CHOH), sorbitol ((CH2OH)2(CHOH)4), and vinyl alcohols ((HCOHCH2)n) as plasticizers for keratin, a peptide-based biopolymer. Yet, these plasticizers are not nitrogen-containing plasticizers of the present invention and, in general, are not ideal. Because of the thermal stress that occurs during extrusion to form keratin composites, polyols can lose a water molecule. Glycerol, for example, can lose a water molecule, causing formation of glycidol, a thermally unstable and therefore chemically reactive compound. This will result in unwanted side reactions with sites in the biopolymer substrate. Glycidol is a potential carcinogen, and is volatile, especially above its boiling point of 167° C. Thus, any glycidol formed that remains unreacted during extrusion could be released into the air upon leaving the extruder. Also, some glycerol can leach out of biopolymer formulations causing the biopolymer to have a greasy feeling when touched/handled.
It is well-established that lactating dairy cows often have amino acid deficiencies, especially lysine which is present in high concentration in milk. Feeding rumen-protected lysine, methionine, and histidine to dairy cows result in increased milk protein yield. (Lee, et al., J. Dairy Sci. 95:6042-6056 (2012)) The prior art is full of attempts to increase the amount of amino acids available to cows to increase their absorption of the amino acids.
U.S. Pat. No. 5,720,970 discloses a feed additive containing lysine and/or methionine covered in a protective coating of lecithin, at least one inorganic substance which is stable in neutral pH conditions and soluble under acidic conditions, and either C14-C22 monocarboxylic acids, hardened vegetable oils, hardened animal oils, and/or waxes. The goal of this feed additive is to allow the lysine and/or methionine to pass through the rumen undigested and then release the lysine and/or methionine in an environment conducive for absorption of the amino acids. U.S. Pat. Nos. 5,720,970 and 5,871,773 also disclose that one should introduce the amino acid feed additive at specific times related to milk production (i.e., for a specific period of time prior to calving and for a specific period of time during lactation). U.S. Pat. No. 5,795,585 discloses a feed additive containing a phosphoric acid salt of a basic amino acid and magnesium, and optionally another polyvalent metal ion. The basic amino acid can be lysine, arginine and ornithine. This feed additive is stable in the rumen and releases the basic amino acids in the abomasum and other lower digestive organs of a ruminant. Yet, these prior art methods of increasing amino acid absorption in the ruminant do not work well, and a need still exists for a method to increase amino acid absorption in ruminants as well as the compositions that are used to increase amino acid absorption.
As such, a need exists for an easy-to-use plasticizer (such as nitrogen-containing compounds having a melting point higher than urea) that can be used with peptide-based biopolymers to make compounds such as fertilizers and animal feed; and lack the problems of using petroleum-based plasticizers or urea.